1. Field of the Invention
The present invention relates to a superconductive conductor which is applied to a superconducting cable, or a current lead for supplying a current to a superconducting element such as a superconducting magnet or the like, and more particularly, it relates to an improvement in arrangement of a plurality of superconducting wires which are included in a superconductive conductor.
2. Description of the Background Art
An attempt has been made in the art to implement a superconducting cable using NbTi or Nb.sub.3 Sn. Such a superconducting cable is cooled by liquid helium. This type of superconducting cable is merely evaluated in property as a relatively short cable for experimentation.
On the other hand, a normal conductor such as a pipe-shaped copper conductor or a brass conductor is applied to a current lead for supplying a current to a superconducting element such as a superconducting magnet. Such a current lead is put into practice as an element for carrying a current to a superconducting magnet using NbTi or Nb.sub.3 Sn, for example. The current lead is so designed that its one end, which is connected to the superconducting magnet, is cooled by liquid helium for cooling the superconducting magnet while a portion upwardly projecting beyond the level of the liquid helium is efficiently cooled by evaporating helium gas.
However, the conventional superconducting cable must be cooled by liquid helium as described above, and hence it is necessary to cover the periphery of the cooled portion with heat insulating material in a high vacuum. Further, the running cost is increased due to employment of the liquid helium.
On the other hand, the conventional current lead is formed by a normal conductor using copper or brass, which has high thermal conductivity. Joule loss is caused due to a voltage drop of the member itself upon energization and that caused by contact resistance between the used members, to generate heat. This heat exerts influence upon a cooling medium such as liquid helium in which the superconducting magnet is dipped, whereby the cooling medium evaporates by conduction of the heat.